Warming Is Turning Tundra into Forests

Global warming turns tundra to forest: study

Reuters, June 3, 2012

(Reuters) - Plants and shrubs have colonised parts of the Arctic tundra in recent decades growing into small trees, a scientific study found, adding the change may lead to an increase in global warming pressures if replicated on a wider scale.

Scientists from Finland and Oxford University investigated an area of 100,000 square km, roughly the size of Iceland, in the northwestern Eurasian tundra, stretching from western Siberia to Finland.

Using data from satellite imaging, fieldwork and observations from local reindeer herders, they found that in 8-15 percent of the area willow and alder plants have grown to over 2 metres in the last 30-40 years.

A report of the research is published on Sunday in the journal Nature Climate Change.

"It's a big surprise that these plants are reacting in this way," said Marc Macias-Fauria of Oxford University and lead author of the report.

Scientists had thought that the colonisation of the warming Arctic would take centuries, he said.

"But what we've found is that the shrubs that are already there are transforming into trees in just a few decades."

Previous studies suggested that the advance of forest into Arctic tundra could increase Arctic warming by an extra 1-2 degrees

Celsius (1.8-3.6 Fahrenheit) by the late 21st Century.

Warming in the Arctic is happening about twice as fast as in the rest of the world. As reflective snow and ice recede, they expose soil or water which are a darker colour and so soak up more of the sun's heat.

The same occurs when trees are tall enough to rise above the snowfall, presenting a dark, light-absorbing surface.

More warming in the Arctic is likely to spur oil and gas development, as well as attracting herds of reindeer as they feed on willow shrubs.

But a warming planet is also linked to increases in severe drought and flooding around the world, putting people, crops and livestock at greater risk.

The global average temperature last year was the ninth-warmest in the modern meteorological record, continuing a trend linked to greenhouse gases that saw nine of the 10 hottest years occurring since the year 2000, NASA scientists said in January.

Macias-Fauria said the area researched in the study is a small part of the vast Arctic tundra, and an area that is already warmer than the rest of the Arctic, likely due to the influence of warm air from the Gulf Stream.

"However, this area does seem to be a bellwether for the rest of the region, it can show us what is likely to happen to the rest of the Arctic in the near future if these warming trends continue."

Tundra Shrubs Turn into Trees as Arctic Warms

LiveScience, June 3, 2012

Tundra is by definition a cold, treeless landscape. But scientists have found that in a part of the Eurasian Arctic, willow and alder shrubs, once stunted by harsh weather, have been growing upward to the height of trees in recent decades.

The reason for the change: the warming Arctic climate, they say.

Roughly 30 years ago, trees were nearly unknown there. Now, 10 percent to 15 percent of the land in the southern part of the northwestern Eurasian tundra, which stretches between Finland and western Siberia, is covered by new tree-size shrubs, which stand higher than 6.6 feet (2 meters), new research indicates.

"What we have found essentially is that the growth of these shrubs is really linked to temperatures," said study researcher Marc Macias-Fauria of Oxford University's Biodiversity Institute. "They are reacting to warming temperatures by growing more."

The change first came to the attention of scientists when nomadic reindeer herdsmen, the indigenous Nenets, said they were losing sight of their reindeer in the new trees, Macias-Fauria said.

Until recently the shrubs common in this part of the Arctic stood at most about 3.3 feet (1 meter) high, too low to obscure a reindeer.

To better understand the climate dynamics associated with the increase in growth in the northwestern Eurasian tundra, he and colleagues studied information from the herdsmen's observations, temperature data, growth rings in the wood of shrubs and satellite data, including observations of the amount of green covering the landscape during the growing season.

They found the shrubs grew most in years with warm Julys.

To determine how much of the land is now covered by the treelike shrubs, they used high-resolution satellite images, verifying what they saw in these with trips out into the field.

Shrubs are common in the southern parts of treeless tundra regions, giving way to more grasses, lichens and mosses farther north. Harsh Arctic weather generally prevents the shrubs from growing up —"the bigger you are, the more exposed you are to the atmospheric conditions," Macias-Fauria said.

This Eurasian piece of the Arctic is among the mildest Arctic regions, so it may offer a hint as to what is to come in other places, he and his colleagues point out.

Were the treelike shrubs to become widespread, this change could exacerbate global warming through what is known as the albedo effect, he said. When snow falls on the tundra's shrubs, it creates a continuous white blanket that reflects the sun's energy back out into space. Trees, however, rise above the snow, breaking up the white and darkening the land surface. As a result, less energy is reflected back into space and more is absorbed, resulting in warming.

The loss of Arctic white sea ice over dark ocean has a similar effect.

Eventually, it is believed that warming will cause the forest to the south to creep north into what is now tundra. However, that process is expected to take much longer.

This research is detailed online today (June 3) in the journal Nature Climate Change.